Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.56	4.185%	$83.9314	$83.93	$83.95	$83.90
Purchase #2	$60.72	5.239%	$63.9011	$63.90	$63.90	$63.90
Purchase #3	$17.84	4.616%	$18.6635	$18.66	$18.65	$18.70
Purchase #4	$144.72	9.147%	$157.9575	$157.96	$157.95	$158.00
Purchase #5	$176.35	4.628%	$184.5115	$184.51	$184.50	$184.50
Purchase #6	$130.91	10.297%	$144.3898	$144.39	$144.40	$144.40
Purchase #7	$150.78	9.592%	$165.2428	$165.24	$165.25	$165.20
7 purchase totals =	$761.88		$818.5976	$818.59	$818.60	$818.60